This invention relates generally to cooling systems for turbine modules and more specifically to high pressure cooling air systems for turbine modules in recuperated gas turbine engines.
The durability and performance of a gas turbine engine is directly related to the life and efficiency of the high pressure turbine (HPT) module components. Under normal operating conditions for gas turbine engines, the engine turbine components are exposed to extreme temperatures, which in time, have the potential to cause distress, reduce engine efficiency and reduce service life. If the engine is allowed to operate at these extreme temperatures the increased thermal expansion and contraction of these components adversely affects clearances and the relationship between components with different coefficients of thermal expansion. Consequently, these components must be cooled to avoid potentially damaging consequences at elevated operating temperatures. In a non-recuperated gas turbine engine, a portion of the compressed air from the main flow path is extracted at the output of the compressor, upstream of the combustion chamber, for cooling the HPT module components. When a recuperator is added to the thermodynamic cycle of the engine, the temperature of the compressor discharge air is elevated hundreds of degrees, as it passes through the recuperator. Therefore, the recuperator discharge air is too hot and does not have the capability to provide adequate cooling to meet the HPT module requirements.
A cooling system for a recuperated gas turbine engine is described in U.S. Pat. No. 3,907,457. In the '457 patent, a portion of compressed air from the main air stream is diverted around the combustion chamber to cool the bearing chamber. However, the air is diverted through the high temperature side of the engine, resulting in increased temperatures of the cooling air. This design therefore compromises the effectiveness of the cooling air.
An alternative cooling system for a gas turbine engine is described in U.S. Pat. No. 3,204,406. In the '406 patent, the cooling system delivers cooling air to the internal part of the engine from the compressors through conduits. In areas where high pressure is required, part of the conduit is routed externally through an intercooler to maintain the required temperature and pressure. This adds external plumbing which, in turn, adds weight while each external connection provides a potential leak path. The tortuous internal conduits described in the '406 patent are also susceptible to blockage and seal leakage.
As can be seen, there is a need for a cooling system for recuperated gas turbine engines that is efficient and straightforward in design.